There are 70 species of Diascia endemic to South Africa found mostly in the eastern regions including Lesotho, Transkei, Orange Free State, Natal and Eastern Cape Province. The latter in which mostly annuals are found.

Diascia is derived from the Greek words, di, two, and askos, sac, referring to the pair of translucent yellow sacs/windows in the corolla and not to the two spurs which are absent in the type specimen D. bergiana. In most annuals, Diascia species follow this example, but in the perennials, the window is single or only slightly doubled. This double spur, though, is a striking characteristic of many Diascia species. The spurs contain glandular hairs which secrete fatty oil. In some species, small dark patches of these tiny glands are also found on the face of the flower. The oil is harvested by members of a genus of bee which evolved to reach into the spurs of the flower.

Many of the collections of D. vigilis come from the valley of the Tugela River and its name is derived from an area landmark, The Sentinel. The Sentinel (the Latin word is vigil ) is a huge basalt rock on the northern end of The Amphitheatre in the Royal Natal National Park.

Diascia elegans is in fact D. vigilis. This epithet was an unpublished name, provisionally used while the genus was being studied, and to avoid confusion, should not be used.

The earliest record of Diascia vigilis is in 1895 when Thode cited the species at Witzieshoek, Caledon Pass in the Orange Free State. Hilliard & Burtt recorded the species in the Orange Free State and Natal, and accessioned specimens of D. vigilis were housed in the Royal Botanic Garden, Edinburgh in 1981 and 1982.

Diascia vigilis is similar to D. anastrepta with upward-pointing spurs. Other species common to gardeners either through hybridization or selection include D. rigescens, D. integerrima, D. fetcaniensis and D. mollis